These days, stringent exhaust gas- and fuel economy-related regulations are being implemented on internal combustion engines such as automobile engines. A turbocharger is an example of techniques adopted for fuel economy improvement and a reduction in the concentration of CO2 in exhaust gas.
The turbocharger is a rotary machine rotating an impeller of a centrifugal compressor as a turbine is driven to rotate by exhaust gas from an engine. Air compressed by the rotation of the impeller is boosted in pressure by being decelerated by a diffuser and is supplied to the engine through a scroll flow path.
Effective in the interest of the efficiency of the turbocharger (turbocharging efficiency) is a minimized clearance between the impeller of the compressor and a housing covering the impeller. Fluid counterflow from a high pressure side to a low pressure side of the compressor can be increasingly suppressed as the clearance is reduced, and then the efficiency of the turbocharger as a whole is improved.
An abradable seal such as that disclosed in PTL 1 is practically used as a technique for reducing the clearance between the impeller and the housing as described above. The abradable seal is formed from a machinable material that is softer than the impeller because it might be brought into contact with the impeller. Preferred examples of the material include polytetrafluoroethylene (Teflon (registered trademark)). The abradable seal is obtained, with a desired shape and prior to attachment to the housing, by that type of resin material being injection-molded. PTL 1 discloses a configuration in which the abradable seal formed from Teflon (registered trademark) is press-fitted to a groove portion of the compressor housing and is fixed by a curable gasket. In the above-described device, press fitting for ensuring abradable seal attachment accuracy is performed at this time such that a surface (positioning surface) of the abradable seal becomes flush with a reference surface disposed on the housing side. As a result of the press fitting, abradable seal positioning accuracy in an axial direction of the turbocharger can be increased and post-processing (cutting processing) for the abradable seal can be omitted.